Dental tool



Nov. 15, 1955 E. P. OBERLEY 2,723,455

DENTAL TOOL.

Filed July 29, 1954 INVENTOR ERNESTPAUL OBEl-PLE) A'ITORNEY United States PatentC DENTAL TOOL Ernest Paul Oberley, Mineola, N. Y.

Application July 29, 1954, Serial No. 446,546

1 Claim. (Cl. 32-49) This invention relates to dental toolsparticularly to rotating cutting instruments used in the preparation of teeth for crowns.

Conventional cutting toolsof the above category, despite their universal adoption, have certain inherent shortcomings which render their use difficult, especially in the procedure for producing smooth axial or lateral surfaces, preparations without undercuts and in proper parallel relation to preparations on other teeth for an unobstructed draw, and definite regular margins at the desired depth under the free gum margin. It is axiomatic in the art that unless there is the required smoothness and definition of the prepared toothwithout leaving excess material or performing excess cutting-the tooth is difficult to impression, and good fitting crowns cannot be produced. 7

With conventional side-cutting cylinders, cones, discs and burrs, great skill and diligent care must be exercised by the operator to avoid excessive cutting in a pulpal direction to cause undesirable shoulder and surface irregularities; and when operating under the free gum margin considerable caution must be employed to avoid producing irregular or overextended margins, or severing the gingival attachment tothe lo oth. 7 Moreover, with said conventional instruments. there is the ever-present danger of overreduction of teeth due to several additional factorsthe inability actually to see the area being reduced by the tool, the use of high-speed and fast-cutting abrasives that reduce the tooth structure rapidly, and the application of varying cutting pressures depending upon the hardness of the tooth structure or such extraneous forces as pressure applied to the operators hand or instruments by the patients tongue, lips or cheeks.

Aside from the above-mentioned difficulties of accurate cutting with conventional instruments, there is the further danger of abrading and lacerating of the gingival tissues when the cutting is carried below the gingival margineven if light pressure is used. Indeed, with conventional disc-type instruments, the accidental cutting of tongue, lips and cheeks is not an infrequent occurrence. Some attempt has been made to reduce this danger by providing one smooth side on 'the conventional disc-type instrument, and a smooth terminal end on the conventional cylinder-type stone; but it has been found that such single safe surfaces do not prevent gingival'laceration and abrasion caused by the peripheral edges of the tool the edges that define the juncture between the cutting and the smooth surfaces of the instrument.

It is primarily within my contemplation to provide a rotating cutting instrument of the above-mentioned category having none of the aforesaid shortcomings. Specifically, it is my primary objective to provide a dental tool that will reduce the degree of skill and diligence that has heretofore been required with conventional instruments in the production of satisfactory tooth preparations, my secondary objective being to permit the automatic guiding of the grinding process beyond the normal ice free gum cufi with minimum laceration of the gingival tissues.

In that aspect of my invention which relates to the accuracy of the cutting process, it is my object to provide a novel tooth having two main features, (1) the signalling feature, by virtue of which the operator is able to sense the time when he is to cease applying cutting pressure, and (2) the self-limiting feature, by virtue of which the cutting action of the tool automatically stops at a predetermined point, thereby reducing the need for dependence upon visual perception. In the accomplish ment if this objective, a peripheral limiting or guiding surface is employed which, as it operatively contacts the tooth, stops the cutting action of the instrument to prevent the overreduction of tooth structure, the establishment of undesired ridges, shoulders and irregularities, and the extension of margins to excessive depths beyond the gingival margin. I have observed that my novel tool readily follows the tooth contour at the gingival region, resulting in a preparation that is smooth and free of irregularities; and I have found that its use insures preparations which are easy to impression and that permit the accurate fitting of crowns. I have also found that instruments according to my invention are easy to control, particularly since any excessive pressures that tend to cause an overreduction of the tooth are resisted by the limiting or guiding surface of the tool as soon as the cutting action has gone to a predetermined depth; and because of such insurance against overreduction, there is a corresponding reduction in trauma caused by such excessive cutting.

In that aspect of my invention that relates to the safety factor, it is my object to provide a tool with compound safe surfaces, instead of the above-mentioned single" safe surface. In the accomplishment of this object, an abrasive-free portion is provided on said limiting or guiding surface and continuously therefrom to the maincutting side or surface of the toola novel arrangement which permits a compression or displacement of the gingival tissue, with a minimum of abrasion thereof, enabling the safe grinding of the preparation to a level below the normal free gum margin.

Other objects, features and advantages will appear from the drawings and the description hereinafter given.

Referring to the drawings,

Figure 1 is an enlarged side elevation of my invention as applied to a side-cutting cylinder, a fragment of the shank being shown.

Figure 2 is a bottom view of Figure l.

- Figure 3 is a greatly magnified fragmentary section of Figure 2 taken along line 33.

Figure 4 is an enlarged fragmentary elevational view of a tooth to be prepared by the tool of Figures 1 to 3, the adjacent gum portions being shown in section, the dot-dash lines showing the original outline of the tooth, the full line outline showing the tooth after a preliminary preparation where the upper portion of the tooth has been removed by a conventional tool, the dotted line showing the position of the proposed preparation on the lateral surface of the tooth.

Figure 5 is another elevational view of the tooth of Figure 4, showing the tool of Figure 1 operatively in place at the beginning of the process of preparing the tooth, the gum being shown operatively depressed by the tool.

Figure 6 is a view like Figure 5, showing a portion of the tooth removed during the grinding process.

Figure 7 is a view like Figures 5 and 6, but showing the position of the tool when the reduction has bee automatically stopped by the limiting surface of the tool.

Figure 8 is a view substantially like Figure 7, but showing the tool in a somewhat raised position.

In the form of my invention shown in Figures 1 to 3, the shank supports the tool proper 41, comprising an abrasive or cutting portion 42 and a terminal or noncutting portion 43. In this form of my invention the body portion 44 has an annular recessed wall 45 within which is disposed an annular cylinder or layer of abrasive material 46. The said lower or terminal portion 43 has a smooth. outer limiting surface 47 which, in this form of my invention, is substantially flush with the outer surface 48 of the abrasive wall 46. The lowermost terminal sur face 49 of the tool is flat and smooth, the peripheral juncture 50 between limiting surface 47 and terminal surface 49 being convexly rounded.

The application of this tool is illustrated in Figures 4 to 8. Figure 4 shows the tooth 51 that had been reduced, by a preliminary process employing a conventional cutting tool, to the shape ready for the operation to be performed by tool 41. The dot-dash outline 52 represents the original contour of the tooth-the full-line outline 53a showing the contour of the tooth after said preliminary preparation. The adjacent gum portions 53 and 54 are shown flanking the tooth, the gingival crests 55 and 56, respectively, being shown in their original or normal positions. It will be observed that the margin of preparation, designated by the reference numeral 57, is below the said crest. A portion of the lateral surface to which the cutting action is to be limited, in accord ance with the proposed preparation, is represented by the dotted line 58the portion of the tooth to be removed by the tool being designated by the reference numeral 59.

Figure 5 shows the tool 41 at the beginning of the process. It will be observed that terminal portion 43-which serves as limiting and guiding means, in a manner to be hereinafter described-presses the gum 53 downwardly, the pressing action being effected by the smooth lower surface 49. Since there is no abrasive on the said terminal portion 43, and since the said corner 50 is rounded, there is a minimum of abrading action of the tool upon the compressed gum 53.

The operating pressures are in a downward direction A and a pulpal direction B. As pressure is applied and the grinding action takes place, the portion to be re movedthe protuberance 59-is gradually ground away, as indicated in Figure 6, the lower surface 49 of the tool rotatably and slidably moving upon the upper portion of the gum section 53. It will be noted, in the position of the tool shown in Figure 6, that the said terminal portion 43 is entirely out of engagement with the tooth 51,

only the abrasive portion 42 being in engagement with the tooth-the space 60 separating the annular surface of terminal portion 43 and the tooth proper.

However, when the said terminal portion finally comes into engagement with the tooth 51, as shown in Figure 7, no further grinding progress, in a pulpal direction, can take place, in view of the fact that said annular limiting surface 47 contains no abrasive thereon. In other words, When the upper circumferential portion 61 of said limiting surface comes into engagement with said margin of preparation 57, there can be no further inward or pulpal grinding of the tooths axial surface, since the smooth limiting surface 47 is incapable of effecting any cutting of the tooth. It is thus at this point that the operator senses, by tactual experience, that grinding has ceased. He therefore merely moves the instrument circumferentially about the lateral surface of the tooth, to the next adjacent region, and continues the grinding action at that point.

The operation above described is repeated for each successive lateral section of the tooth, the grinding action discontinuing when the limiting surface 47 of the tool comes into engagement with the tooth. With each step of the process, the abrasive portion 42 performs its cutting action in conventional manner, and when said limiting surface, or any'portion thereof, such as portion 61, engages the tooth, it merely smoothly rides therealong, without any cutting action. The operator senses this action-as a signal to discontinue grinding pressure and move the tool circumferentially to different positions about the tooth in the process of preparing the surface thereof. The tool thus accomplishes its intended twofold objective-it automatically effects a cutting of the tooth surface up to a predetermined region, without any possibility of cutting therebeyondand it signals the operator to proceed to an adjacent cutting area or to stop the action, without any need to resort to visual inspection.

It will be observed that the height of the lateral limiting surface 47 of terminal portions 43 represents but a small fraction of the total height of the cylinder. The height of said limiting surface is determined by experience, and is dependent upon the distance of the margin of preparation 57 below the gingival crest 55. Based upon such experience, which is within the realm of general dental knowledge, the height of said limiting surface 47 is determined. Hence, with an accurate predetermination of said height, the upper circumferential portion 61 of limiting surface 47 will automatically determine the lowermost cutting point of the tool to the margin of preparation, without visual guidance.

In the above description, the invention has been disclosed merely by way of example and in preferred manner; but obviously many variations and modifications may be made therein. It is to be understood, therefore, that the invention is not limited to any specific form or manner of practicing same, except insofar as such limitations are specified in the appended claim.

I claim:

In a rotary dental tool, a body portion having a substantially cylindrical operative tooth-engaging surface, said surface comprising a cutting portion and a smooth annular non-cutting limiting portion adjacent a terminal of said body portion, said cutting portion comprising a substantially cylindrical recessed portion and a layer of abrasive material within said recessed portion and presenting an outer cutting surface substantially flush with said annular limiting portion.

Great Britain Aug. 25, 1932 Great Britain Aug. 12, 1953 

